The present invention relates to a mechanism for converting a cross-sectionally substantially U-shaped web of wrapping material into a wrapping tube by welding together the longitudinal edges of the web by moving the latter against one another and through a welding device.
In the commonly owned U.S. Pat. No. 4,299,075, dated Nov. 10, 1981, a wrapping apparatus is described having forming means imparting to webs of wrapping material of U-shaped cross section as these pass through the forming means. From the forming means the webs of wrapping material are moved through longitudinal welding means for welding together the longitudinal edges of the webs. The wrapping apparatus works with webs of wrapping material coated with a weldable material. Such a wrapping material is sufficiently rigid to be self-supporting between the forming means and the longitudinal welding means, with the effect that the guidance of the longitudinal edges provided by the longitudinal welding means is sufficient to move these against one another after the edges leave the forming means.
In experiments underlying the present invention it has been attempted to use another and far more flexible and "live" wrapping material, i.e. in the form of strips of thin plastic film. It was found, however, that owing to lack of rigidity this material is not sufficiently self-supporting to pass in a freely suspended state from the cross-sectionally substantially U-shaped form to a tubular shape, i.e. with the longitudinal edges abutting one another.